Because of disadvantages existing with respect to angular position sensors, such as slow data sampling rates, there exists a need in the art for an improved angular position sensor that is capable of accurate dynamic angle measurements. In particular, an improved angular position sensor is needed in shaft alignment systems. Furthermore, there exists a need for an angular position sensor which is capable of nullifying dynamic error anomalies associated with dynamic angle sensing. Additionally, there is a need for an alignment system including an angular position sensor that is easier to set up and use and which reduces the error in measurement and other problems which inherently result from the design of prior art devices.
The present invention overcomes the difficulties and disadvantages of the prior art by providing an angular position sensing apparatus for mounting on a rotatable body operable to determine an angular position of the rotatable body relative to a point in space. The apparatus utilizes a first dual-axis accelerometer having a first sensing axis for sensing a first acceleration component and a second sensing axis for sensing a second acceleration component. The first and second sensing axes are in substantially perpendicular relation, the first dual-axis accelerometer operable to output a first signal proportional to the sensed first acceleration component and to output a second signal proportional to the sensed second acceleration component. The apparatus also includes a second dual-axis accelerometer having a third sensing axis for sensing a third acceleration component and a fourth sensing axis for sensing a fourth acceleration component. Accordingly, the third and fourth sensing axes are in substantially perpendicular relation, the second dual-axis accelerometer operable to output a third signal proportional to the sensed third acceleration component and to output a fourth signal proportional to the sensed fourth acceleration component. It is preferred that the first and second dual-axis accelerometers are mounted in spaced apart relation on a printed circuit board defining a plane of reference. The apparatus also utilizes a microprocessor operable to determine the angular position of the body as the body rotates through a plurality of angular positions by selecting a fifth signal dependent on the first and third signals or a sixth signal dependent on the second and fourth signals, and determining the angular position of the rotatable body therefrom.
In one embodiment, an accelerometer based angular position sensor is used in an alignment system for aligning a centerline of a first shaft with a centerline of a second shaft. The shaft alignment system includes an analyzer having memory and a sensor head disposed on a mounting bracket and extending in a substantially perpendicular orientation with respect to the centerline of the first shaft. A collimated light source is mounted on the sensor head for transmitting a beam of energy in a direction that is substantially parallel to the first shaft. A photosensitive sensor is also mounted on the sensor head for sensing light and generating a position signal corresponding to a position of a light beam impinging upon the photosensitive sensor. The angular position sensing apparatus includes at least one accelerometer for generating a signal corresponding to the angular orientation of the sensor head with respect to the first shaft, and a microprocessor processes the angular position sensor signal generated by the angular position sensor, providing an output corresponding to the angular position of the sensor head relative to the first shaft.